This application claims the priority of German patent document 102 14 868.6, filed Apr. 4, 2002, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for monitoring parameters of an easily ignited gas.
Electronic units, typically integrated in controllers, are used increasingly for open-loop control, closed-loop control and/or monitoring of fixed and mobile devices and systems. During monitoring, relevant status variables of a system are usually measured or observed, and evaluated by means of diagnostic algorithms to predict failures, so that corresponding measures for eliminating or minimizing their effects can be initiated. As a result, environmental risks can be alleviated.
In fuel cell systems used, for example, in vehicles, electrical energy is generated from gases which are rich in hydrogen and oxygen. Because hydrogen is an explosive gas, reliable monitoring of the concentration of the hydrogen is essential. Oxygen can be ignited, for example, at concentrations starting from approximately 4%.
German patent document DE 199 59 699 C1 discloses a device for monitoring a gas which is rich in hydrogen in a vehicle with a fuel cell system. The device has an evaluation unit to which hydrogen-sensitive sensors are connected. The latter are arranged in two ducts and are connected, at least partially, in the form of a cascade, providing a device which is robust with respect to fluctuations in temperature.
In order to ensure the operational capability and the safety of a fuel cell system (or other systems in which a gas that is rich in hydrogen or other easily ignited materials are used, such as internal combustion engines to which hydrogen is fed as a fuel), it is necessary to monitor such system for an acceptable concentration of hydrogen (or other easily ignited gas), both in a state of rest and while the entire system is operating. Such monitor must be performed as long as hydrogen (or other easily ignited gas) is present in the system, in particular in a store or tank. As used herein, easily ignited gases include combustible, explosive or highly inflammable materials or mixtures of such materials, such as hydrogen.
One object of the invention is to provide a device for monitoring concentration of an easily ignited gas during periods when the system is at rest, with a low expenditure of electrical energy.
Another object of the invention is to provide a fuel cell system and a means of transportation in which an easily ignited gas can be monitored with a low expenditure of electrical energy.
Still another object of the invention is to provide a method for monitoring an easily ignited gas, with a low demand for electrical energy.
These and other objects and advantages are achieved by the method and apparatus according to the invention in which the hydrogen concentration is monitored during a state of rest, in such a way that a current/voltage source, such an energy store, provided for the entire system is only slightly loaded; and as a result it is prevented from being stressed. Entire systems include, for example, a fuel cell system or a means of transportation, such as a motor vehicle.
The invention can advantageously be used in a motor vehicle to detect gas leakages, due to the low energy demand of a wake-up device for the monitoring unit, even when the motor vehicle is not in use, (for example, when it is parked), because the low energy demand of the wake-up device can be covered by a vehicle battery. The safety of persons, vehicle and their surroundings is therefore ensured even when the motor vehicle is in a stationary state or parked.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.